Method for low-temperature cooling, liquefaction, and separation of not easily condensable gases



Feb."l"6 1926. 1,573,752

- A. SELIGMANN I METHOD FOR LOW TEMPERATURE COOL ING, LIQUEFACTION, AND SEPARATION OF NOT EASILY CONDENSABLE GASES Filed March 5. 1924 H pressum 2 7/5 sz mmn/ lll Patented eb. 16, 1926.

UNITED STATES PATENT OFFICE.

ARTHUR SELIGMANN, OF BREMEN, GERMANY.

METHOD FOR LOWrTIEMPERATUBE COOLING, LIQUEFACTION, AND SEPARATION OF NOT EASILY CONDENSABLE GASES.

Application filed March 3, 1924. Serial Nb. 696,595.

T 0 all whom it may concern:

Be it known that I, ARTHUR SELIGMANN, a citizen of Germany, residing at Bremen, Germany, have invented certain new and useful Improvements in a Method for Low- Temperature Cooling, Liquefaction, and Separation of Not Easily Oondensable Gases; and Ido hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art-to which it appertains to make and use the same. A

This invention relates to, improvements in the well known method for low temperature cooling and liquefaction of gases by means of throttling (internalv working) which is based exclusively on the fact that the heat contents of almost all gases at ordinary temperature are lower under high pressure than under atmospheric pressure. It is therefore merely necessary to send the gas under high pressure into an apparatus and to let it fiowout expanded at the same temperature in using a counter-current heat exchanger, known per se, to obtain a refrigerating duty and to come in this manner easily to low temperatures.

In the building of liquefying plants and separation plants it is common practice to make the total expansion take place suddenly in the throttling valve. One believed that the loss of pressure from the'compressor to the throttle valve and from there to the gas outlet must be so low as possible so that-a low velocity of the gas had to be selected.

The present invention starts from other ideas in order to produce improved effects.

In the improved method it is essential that the gas is sent with great velocity through the heat exchanger or at least through 0011- siderable parts of the same, an essential portion of the decrease of pressure at disposal being consumed by pipe friction in front of or behind a throttle valve which is eventually provided.

It is a prevalent error to believe that a gas, when flowing through a pipe conduit, ought to be heated owing to the friction. Just the opposite occurs when the insulation is perfect and when the gas is in the inversion curve. The friction produces heat but not so much as the refrigeration amounts.

to, which is due to the loss of pressure and to the work of expansion-resulting therefrom. Thisis just the characteristic feature of the throttling process explained by the experiments made by Thomson-Joule, Noell and others. The pipe friction is nothing else but a throttling distributed over longer distances.

Theoretically there would be no objection to provide no throttling. valve at all but to let the total decrease of pressure take place constantly. In practice however a throttling element will be preserved for regulating purposes. There is nothing to prevent that a considerable portion of the decrease of pressure be consumed only. behind the throttling valve on the return travel of the gas through the counter-current apparatus, at

least not if real refrigeration or liquefaction is in question. For the separation of the gases'the condition has to be taken into consideration that the column 'or other separating apparatus works worse at higher pressure. The proceedings in the interior of the apparatus arein any case of no account for the heat balance.

The invention has for its main purpose to improve the heat transmission by the lncreased velocity which is admissible and to permit that the pipes of the counter current apparatus be made narrower and consequently lighter.

The pipes may be made lighter with decreasing diameter as can be easily seen from the following elementary consideration.

s the thickness of the pipe walls,

Z the pipe length, r

y the specifi weight of the material,

is, its admissible tensile stress intensity,

l p the gas pressure decisive for the calculation of the pipes,

F the required heatexchanging surface,

G the Weight of the pipes, the following equations must evidently be valid:

is the average pipe diameter,

The gas velocity may be easily increased so that, notwithstanding the increase of volume of the gas due to the decrease of pressure, the cross section of the free passage can nevertheless be still reduced, or more correctly expressed the-reduction of the cross setcion is just the constructive means to enforce the desired velocity. Equation No. 4-. shows however that the weight of the pipes would be reduced with decreasing diameter even if the required heat exchanging surface remained unaltered. v

It is common knowledge that the coefficient of heat transmission is considerably improved by increasing the gas velocity. On the other hand it is true that it increases with the decreasing specific weight of the gas but it is possible to increase, accordin to the improved method, the veloci ty of tie gas in a much higher degree than its specific volume and as according to the.

methods hit erto known. The economy in weight is furt er increased by the fact that the necessary heat exchanging surface is also reduced, as can be seen from equation N o. 4.

The advantages are generally known which result from the lighter construction as regards cost of manufacture, losses from insulation, time for getting ready and so on.

It is scarcely necessary to point out that the above co sideration holds good even when, besides the refrigerating duty produced by throttling, a further refrigerating duty is providedwhich is produced by a freezing mixture, by a cold vapour machine,

expansion with performance of outer workor by ,any other means.

In the accompanying drawing an apparatus for the low temperature cooling and liquefaction of gases according to the invention is diagrammatically shown.

It consists of a countercurrent heat exchanger a and of a separation apparatus (column) b. The gas enters at c with 20.0 atnniinto the narrow pipe conduit d, undergoes on its travel to the throttle valve 6 a decrease of pressure up to about 100 atm., is throttled to about 1.3 atm. and leaves the pipe conduit f with 1 atm.

What I claim is:

1. l\/Iethod of low temperature cooling, liquefaction and separation of gases by throttling which consists of inducing the major portion of the decrease of pressure by causing the gases to flow at relatively great velocity through pipes in which the decrease of pressure is consumed by friction of the gases occurringover the entire length of the walls of the pipes.

2. Method of low temperature cooling, liquefaction and separation of not readily condensable gases by means of throttling, which consists of inducing the entire drop of pressure by causing the gases to flow at relatively great velocity through pipes in which the decrease of pressure is caused by friction of the gases on the entire length of the wallsof the pipes.

3. Method of low temperature cooling, liquefaction and separation of not readily condensable gases by means of throttling, which consists of distributing the major portion of the drop of pressure over a relatively long stretch of flow by causing the gases to flow through relatively narrow and relatively long pipes.

In'testimony whereof, I aflix my signature. v I

ARTHUR SELIGMAN N. 

